Worldwide rebirth of interest in superconducting apparatus is traceable to discovery of high T.sub.c superconductors. In contrast to the .sup..about. 20K. improvement in T.sub.c realized over the period from the discovery of superconductivity in 1911 to last year, superconductors introduced over the past few months have seen a rise in critical temperature through the 77 K. boiling point of liquid nitrogen and well into the 90-100 K. range. Based on anomalies in magnetic susceptibility and resistivity, both relative to changing temperature, evidence for superconductivity has been reported at temperatures as high as 240 K. (See J. T. Chen et al., "Observation of the Inverse dc Josephson Effect at 240 K.", to be published.) Copending U.S. application, Batlogg-Cava-VanDover 2-4-7, Ser. No. 021,229, filed Mar. 3, 1987, describes and claims the generic chase of materials to which work has generally been directed. Chemically, the category is described by the nominal formula M.sub.2 M'Cu.sub.3 O.sub.9-.delta.. The detailed requirements of members of the class are set forth in the copending application. Much of the work reported is based on material of the approximate composition Ba.sub.2 YCu.sub.3 O.sub.7 sometimes referred to simply as barium-yttrium-copper oxide.
While many structures and processing utilizing superconductivity have been described in the literature, over the years prevalent use has awaited critical temperatures high enough for expedient cooling. Now that liquid nitrogen cooling is a reality attention is being refocussed on these uses. The present invention is directed to structures and processes which depend on separation brought about by coupling of a superconducting member and a magnetic member. While the concerned apparatus may be static by nature, other forms involve one or more moving elements.
One type of apparatus that has received considerable attention depends upon levitation. A variety of such applications are described in "Superconducting Machines and Devices--Large Systems Applications."
Another such application takes the form of a superconducting bearing (see Applied Superconductivity, Vol. II).
Levitation demonstrations at liquid nitrogen temperatures began appearing shortly after announcement of the new high T.sub.c materials. A demonstration that received considerable attention in the press takes the form of a cup-shaped superconducting member suspending a small permanent magnet (see Physics Today, April, '87, cover). Such demonstrations have, consistent with earliest work, depended upon geometric shapes or other means designed for lateral stabilization. The cup walls represent a typical geometric design intended to offer lateral constraint for this purpose.